The stackup
A thin dielectric over aluminium conducts heat from the LED pad into the base. Thicker dielectric isolates better but conducts less; the choice follows the isolation class and the thermal model.
Thermal vias and pads
Direct thermal pads and filled vias shorten the path. Specify their diameter and pitch so the assembly and the board are designed together.
Long-life fixtures
For street and industrial lighting, thermal cycling over years matters more than the initial junction temperature. Ask for the stackup and the thermal resistance, then test a prototype at rated power.
